Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site sdcsvax.UUCP Path: utzoo!linus!philabs!cmcl2!seismo!lll-crg!dual!qantel!hplabs!sdcrdcf!sdcsvax!davidson From: davidson@sdcsvax.UUCP (Greg Davidson) Newsgroups: net.physics Subject: Re: QM and Multiple Worlds Message-ID: <1094@sdcsvax.UUCP> Date: Tue, 10-Sep-85 03:10:12 EDT Article-I.D.: sdcsvax.1094 Posted: Tue Sep 10 03:10:12 1985 Date-Received: Thu, 19-Sep-85 00:52:14 EDT References: <486@talcott.UUCP> <1049@sdcsvax.UUCP> <565@baylor.UUCP> Reply-To: davidson@sdcsvax.UUCP (Greg Davidson) Distribution: net Organization: EECS Dept. U.C. San Diego Lines: 141 Keywords: Quantum Mechanics, Multiple Worlds, Reality Summary: Problems raised by Multiple Worlds cannot be lightly dismissed. In an earlier article, I presented problems with the multiple worlds theory (MWT) as an interpretation of quantum mechanical reality. Some of the problems are old, first presented by Bohr, Heisenberg, and other early QM theorists. Some were unconventional ideas suggested by me, with inspiration from a variety of sources. I asked for participation in exploring this often baffling topic. These problems are as much philosophical as physical, as they are constrained by the latter, but must be addressed using the tools of the former. It seems like a good game we can all play, if we're careful to stick to the rules and tread cautiously - this territory is very slippery. Unfortunately, the two postings to reply so far have attempted to dismiss the matter rather than address it. I'll use the most recent as an example. If you read it through, I think you'll see that it was not a responsible posting, although it partially addresses some of my points. The author's text is indented with tabs. My original text indented with >'s. From: peter@baylor.UUCP (Peter da Silva) Subject: Re: QM and Multiple Worlds Date: 28 Aug 85 11:34:34 GMT Organization: The Power Elite, Houston, TX > issue.) A MWT unconstrained by any laws of physics is preferable, > because simpler, to one incorporating laws of physics, hence MWTs > directly do violence to the notion of physics. Now let me answer some How on earth do you figure that an unconstrained MWT is simpler or preferable. The fact that an unconstrained MWT produces a different observed universe than the one we see here is enough to reject that hypothesis. As follows. The conventional MWT, as I understand it, says that each quantum mechanical event splits the universe into a superposition of states, one for each possible outcome. As observers, being restricted to one universe/state, we can observe only one outcome. We infer the existence of superpositions by their effect on the probability of occurrance of events; yet, those superpositions ``collapse'' or ``branch away from us'' (depending on which interpretation you're using) as soon as they interact with our process of observation . Yet all outcomes possible by physical law actually occur in some universe/state. Because we cannot see beyond our own universe/state, we actually have no idea of the true probability of events. We could just happen to be on a very low probability worldline in the state space of branching universes. The universe we wind up in always has a probability value of 1, since we can only observe it after the fact. We cannot predict, since all predicted outcomes always occur. (If you're familiar with the Anthropic Principle in Cosmology, the argument here has a similar [unpleasant] flavor.) We need only extend this line of reasoning a little bit to see that the presence of physical laws constraining the generation of states is also unobservable. Given branching universes, if all possible outcomes of events were to occur, with no physical laws to constrain them, there would be observers along worldlines inferring all kinds of physical laws. Imagine us as such observers, with a deceptive history implying certain physical laws, now being presented with evidence of multiple worlds. What magnificent irony! > Doug Gwyn wrote: > > [1] Not all the alternate worlds are equiprobable! [2] There is no > > observable difference between the alternate-worlds QM and the > > Copenhagen QM. > [1] Maybe, but irrelevant to my point. Also, Occam's razor would suggest > abandoning any theory of structure in the generation of successor worlds. I see. What's happened is that you don't understand Occam's Razor, so you're applying it too broadly. Occams razor simply says that out of (n) hypotheses you should select the simplest and most testable hypothesis so that you know when you're wrong as soon as possible. It doesn't say the simples explanation is right, as you (and the creationists) seem to think. Since your view of how the EWG multiple worlds model works predicts a complete breakdown of causality we know it's wrong (or have you observed this breakdown of causality?). The next thing to do is look at the actual EWG theory. That I'll leave to someone better versed in it than I. The principle you mention sounds like a nice principle for guiding experimentation, but bears no relationship to Ockham's razor. I just checked the Encyclopedia of Philosophy (page 8-307) and found that though I'd spelled his name wrong, I understood his principle quite well. They quote him as saying: ``What can be done with fewer [assumptions] is done in vain with more.'' They go on to say: `The principal use made by Ockham of the principle of parsimony was in the elimination of pseudo-explanatory entities....' Well, in a MWT system, physical laws become pseudo-explanatory entities. No observation can support their existence. I object to your insulting style of argument. You attack my argument by belittling my understanding and comparing me with creationists! Yet you neither check my argument carefully nor offer an alternative. The problem of how to interpret quantum mechanical reality is a real problem. Great physicists tried hard to reject QM because of it. Now that we have been forced to accept QM, we must grapple with it. > For some very interesting reading on these issues, I recommend some > fictional stories designed to present relevant thought experiments. > The earliest I know of are Jorge Luis Borges' stories ``The Garden > of Forking Paths'' which explores the nature of MWTs, and ``The Library > of Babel'', which explains how all possible writings (read `universes') > can be generated by a finite library of books (read `world states'). > Both of these can be found in his collection ``Labyrinths'', New > Directions Pub. Corp., 1964. Last I heard Borges wasn't a physicist. He was not. I recommend his stories for their clear presentation of the philosophical consequences of certain physical models; models which physicists have suggested, but which have neither been accepted nor rejected. You will not find the answers to these problems in existing writings by physicists, you will only find the questions there. > A more recent, and more devastating exploration of MWTs is Larry > Niven's story ``All the Myriad Ways'', in his collection by the same > name [Ballantine Books, 1971], and probably in other collections as > well. Niven never postulated impossible worlds, as you do. His MWT is vanilla EWG. His objection is that EWG makes volition meaningless. He's probably right, but so does determinism. His story is particularly devastating because it sticks closely to the vanilla MWT, yet obtains bizarre results. I'm glad you agree that such models pose serious problems for volition. I would not agree that determinism does. For clear arguments supporting the compatibility of determinism and volition, I recommend Daniel Dennett's new book ``Elbow Room; the kind of free will worth having.'' Its published by MIT Press. Dennett is a professional philosopher who pays close attention to the work of physicists and often collaborates with the physicist and computer scientist Douglas Hofstadter. So how about it folks? Am I the only one disturbed by the philosophical implications of QM? Do you think that physics books have the answers? If you see a hole in my arguments (or Einstein's, for that matter, but check carefully if you think you see a hole in his!), please show me. If I've misunderstood the claims of QM, let me know that too. If you have another interpretation which avoids some of these problems, lets have it! _Greg Davidson Virtual Infinity Systems, San Diego Brought to you by Super Global Mega Corp .com